A hook serves to hook a chain by connecting the distal end of the chain. Thereby, the hook can hang a heavy object by extending a chain. Conventionally, a movable U shape hook or a bi-directional hook is added to hook a selective portion of a chain. A rear hook opening of the U shape hook or the bi-directional hook is used to hook one end of the chain. However other than preparing the U shape hook or the bi-directional hook in advance, the U shape hook or the bi-directional hook will vibrate so that it is unstable and dangerous.